Stable aqueous solutions comprising titanium and zinc and process therewith

ABSTRACT

A composition that can be used as catalyst in esterification, transesterification or polycondensation is disclosed, which comprises a stable solution comprising (a) titanium in the form of a titanium α-hydroxycarboxylic acid or its salt, (b) a C 1 -C 6  carboxylic acid, and (c) zinc in the form of a water-soluble zinc salt, and (d) water; and substantially free of an alkanolamine, an aminocarboxylic acid, or combinations two or more thereof. Also disclosed is an esterification, transesterification or polycondensation process, which comprises contacting, in the presence of the solution composition, an organic acid or its ester or its salt with an alcohol, optionally in the presence of a phosphorus compound, an organic or inorganic toning agent such as cobalt acetate, or combinations thereof.

FIELD OF THE INVENTION

This invention relates to a catalyst composition comprising a stableaqueous solution of organic titanium and zinc complexes and to a processfor using the composition in, for example, esterification,transesterification, or polymerization of a carbonyl compound.

BACKGROUND OF THE INVENTION

Polyesters such as, for example, polyethylene terephthalate,polytrimethylene terephthalate and polybutylene terephthalate, generallyreferred to as “polyalkylene terephthalates”, are a class of importantindustrial polymers. They are widely used in thermoplastic fibers,films, and molding applications.

Polyalkylene terephthalates can be produced by transesterification of adialkyl terephthalate ester with a glycol followed by polycondensationor by direct esterification of terephthalic acid with the selectedglycol followed by polycondensation. A catalyst is used to catalyze theesterification, transesterification and/or polycondensation.

Antimony, in the form of a glycol solution of antimony oxide, frequentlyis used as catalyst in the transesterification or esterificationprocess. However, antimony forms insoluble antimony complexes that plugfiber spinnerets and leads in fiber spinning to frequent shutdowns towipe spinnerets clean of precipitated antimony compounds. Theantimony-based catalysts are also coming under increased environmentalpressure and regulatory control, especially in food contactapplications.

Organic titanates, such as tetraisopropyl and tetra n-butyl titanates,are known to be effective polycondensation catalysts for producingpolyalkylene terephthalates in general, and frequently are the catalystof choice. However, these catalysts tend to hydrolyze on contact withwater, forming glycol-insoluble oligomeric species which lose catalyticactivity. These organic titanates also generate a significant amount ofyellow discoloration when used as polyesterification catalysts.Additionally, many organic titanate catalysts are also substantiallyinsoluble in a polymerization mixture thereby creating non-uniformdistribution of catalyst in the mixture.

U.S. Pat. No. 3,404,121 and U.S. Pat. No. 5,340,907 disclose using acombination of zinc acetate and tetraisopropyl titanate as catalysts.When metal salts such as zinc acetate are added to the reaction mass asa solid, it is difficult to control the feed rate uniformly, resultingin variation of the polymerization conditions. When added as a glycolsolution, the solubility is quite low and the metal may precipitate overtime. The use of a water solution is not compatible with the use oftetraisopropyl titanate because of hydrolysis. Also, water-compatibletitanates, when used as polyesterification catalysts, generatesignificant yellow discoloration in the resultant polymer. See, forexample, EP 812818 and WO 99/28033. There is, therefore, a need for acatalyst system that is compatible with water, has good catalyticactivity, and produces a polymer with reduced color.

Additionally, many solutions of a titanium α-hydroxycarboxylate and awater-soluble zinc salt are not stable, in that they form a cloudysolution or a gel after only a short period of time. This isundesirable, for it may lead to poor control of the catalyst feed to thereaction zone, to an uneven product quality, or to plugging up the downstream spinnerets. Solving this potential problem by adding more wateris undesirable because the added volume makes it difficult to store orship economically. There is also a need for a water-compatible catalystthat has good catalytic activity, produces a polymer with reduced color,is environmentally friendly, does not result in plugging fiberspinnerets, is relatively concentrated, and is stable.

An advantage of the invention is that a titanium- and zinc-containingcatalyst solution can be stabilized for over two weeks under acceleratedstorage conditions of 60° C., equivalent to much longer storage times atambient conditions by inclusion of a carboxylic acid. Other advantagesof the inventive system will become more apparent as the invention ismore fully disclosed herein below.

SUMMARY OF THE INVENTION

A first embodiment of the invention provides an aqueous catalystcomposition which can be used as an esterification, transesterificationor polycondensation catalyst. The composition is a stable solutioncomprising, consisting essentially of, or consisting of (a) titanium inthe form of a titanium α-hydroxycarboxylic acid or its salt, (b) a C₁-C₆aliphatic carboxylic acid, (c) zinc in the form of a water-soluble zincsalt, and (d) water; wherein the solution is substantially free of analkanolamine, an aminocarboxylic acid, or combinations two or morethereof and stable for at least 2 weeks under accelerated agingconditions.

A second embodiment of the invention provides a process, which comprisescontacting, in the presence of a solution composition disclosed in thefirst embodiment of the invention, an organic acid or its ester or itssalt with an alcohol, optionally in the presence of a phosphoruscompound, an organic or inorganic toning agent such as cobalt acetate,or combinations thereof.

DETAILED DESCRIPTION OF THE INVENTION

The stable aqueous solution comprising organic titanium and zinccompounds can be used as catalyst in esterification,transesterification, polycondensation, or combinations of two or morethereof. If used for polycondensation, it can be added to apolymerization medium before or during the esterification,transesterification, or polycondensation step.

According to the first embodiment of the invention, a storage-stablecatalyst composition is provided, which is a solution comprising,consisting essentially of, or consisting of a titaniumα-hydroxycarboxylic acid or salt, a C₁-C₆ aliphatic carboxylic acid, awater-soluble zinc salt and water. By “stable”, it is meant that thesolution is capable of remaining in substantial solution and no visiblecloud, gel or precipitate appears under accelerated storage conditionsfor at least 2, preferably at least 3, and most preferably at least 4weeks wherein accelerated aging conditions comprise storage at 25 toabout 60° C. under about atmospheric pressure. The term “substantial”refers to more than trivial. The term “stable” is also exchangeable with“storage-stable” in this disclosure.

Titanium α-hydroxycarboxylic acid can be prepared by reacting a titaniumorthoester with an α-hydroxycarboxylic acid. The titanium orthoester istypically expressed by the general formula Ti(OR)₄ where each R isindividually selected from an alkyl, cycloalkyl, alkaryl, hydrocarbylradical containing from 1 to about 30, preferably 2 to about 18, andmost preferably 2 to 12 carbon atoms per radical and each R can be thesame or different. Examples of commercially available organic titaniumcompounds include, but are not limited to, TYZOR® TPT and TYZOR® TBT,(tetra isopropyl titanate and tetra n-butyl titanate, respectively),available from E. I. du Pont de Nemours and Company, Wilmington, Del.,USA.

In reaction of a titanium orthoester with an α-hydroxycarboxylic acid,the α-hydroxycarboxylic acid replaces two of the R groups in thetitanium orthoester. Suitable α-hydroxycarboxylic acids include anycarboxylic acid of 1 to 6 carbon atoms comprising carbon, hydrogen andoxygen atoms, and having a hydroxy group in the α-position. Examples ofsuitable α-hydroxycarboxylic acids include, but are not limited to,citric acid, lactic acid, malic acid, tartaric acid, glycolic acid,glyceric acid, α-hydroxybutyric acid, α-hydroxypropionic acid, andcombinations of two or more thereof. The α-hydroxycarboxylic acids arewell known in the art and are disclosed for example in U.S. Pat. No.2,870,181. The reaction can be followed by neutralization with a basesuch as ammonia or an alkali metal, or by reaction with a quaternaryammonium group. The preferred titanium α-hydroxycarboxylate salts aretitanium bis-ammonium lactate, commercially available as TYZOR® LA (in asolution form containing 8.2 weight % titanium) from DuPont, Wilmington,Del., or its sodium salt analogue titanium bis-sodium lactate.

The composition also includes a water-soluble zinc salt. The term“water-soluble” means that it is soluble in more than a trivial amount.Examples of suitable zinc salts include, but are not limited to, zincacetate, zinc chloride, zinc nitrate, zinc sulfate, and combinations oftwo or more thereof. The preferred zinc salt is zinc acetate.

The C₁-C₆ aliphatic carboxylic acid useful for producing the solutioncan be any carboxylic acid that can produce a stable solution of theinvention. It can be the same α-hydroxycarboxylic acid as thosedisclosed above for producing the titanium α-hydroxycarboxylic acid orsalt. Examples of suitable C₁-C₆ aliphatic carboxylic acids include, butare not limited to, formic acid, acetic acid, propionic acid, butyricacid, pentanoic acid, hexanoic acid, citric acid, lactic acid, malicacid, tartaric acid, glycolic acid, glyceric acid, α-hydroxybutyricacid, α-hydroxypropionic acid, and combinations of two or more thereof.The preferred C₁-C₆ aliphatic carboxylic acid is lactic acid.

The inventive solution can contain about 0.1 to about 10, preferablyabout 0.5 to about 10, and most preferably about 0.5 to about 2.5 weight% titanium in the form of a titanium α-hydroxycarboxylic acid or itssalt, or about 5 to about 30 weight % expressed as commercial titaniumbis-ammonium lactate solution (TYZOR® LA). The invention solution cancontain about 0.1 to about 30, preferably about 0.5 to about 30, andmost preferably 0.5-20 weight % zinc in the form of a water-soluble zincsalt. The inventive solution can contain 0.05 to about 10, preferablyabout 0.1 to about 10, and most preferably 0.1 to about 5 weight % of aC₁-C₆ aliphatic carboxylic acid. Water generally can make up the rest ofthe composition. An example of a preferred solution can contain about5-30 weight % titanium bis-ammonium lactate solution (8.2 weight %titanium), about 1-5 weight % lactic acid, and about 20-30 weight % zincacetate, dissolved in water. The purpose of the carboxylic acid is tomaintain an acidic pH, that is, a pH of less than 7 in the inventivesolution. At pH greater than 7, the zinc precipitates.

The inventive solution can include other ingredients, such as aphosphorus compound to improve whiteness, or a cobalt compound to act asa color toner or co-catalyst, providing that they do not adverselyaffect the stability of the solution. For example, the storage-stablesolution can contain about 0 to about 15 weight % phosphorus in the formof a water-soluble phosphorus compound, providing the molar ratio of(titanium plus zinc) to phosphorus is greater than about 1.5. Otheringredients such as cobalt can be present in about the sameconcentration as phosphorus.

The individual components can be combined in any order and the catalystcomposition can be produced by any means known to one skilled in theart. Generally, the mixture can be stirred at a temperature in the rangeof from about 0° C. to about 100° C., preferably about 20° C. to about50° C.

According to the second embodiment of the invention, a process that canbe used in, for example, the production of an ester or polyester isprovided. The process comprises contacting, in the presence of acatalyst composition, an organic acid with an alcohol. The catalystcomposition can be the same as that disclosed above.

A preferred process for producing an ester or polyester comprises,consists essentially of, or consists of contacting a reaction mediumwith a composition disclosed above in the first embodiment of theinvention. The reaction medium can comprise, consist essentially of, orconsist of an alcohol and either (1) an organic acid, a salt thereof, anester thereof, or combinations thereof or (2) an oligomer having repeatunits derived from an organic acid or ester.

The organic acid or ester thereof can have the formula of R¹COOR¹ inwhich each R¹ independently can be (1) hydrogen, (2) hydrocarboxylradical having a carboxylic acid group at the terminus, or (3)hydrocarbyl radical in which each radical has 1 to about 30, preferablyabout 3 to about 15 carbon atoms per radical which can be alkyl,alkenyl, aryl, alkaryl, aralkyl radical, or combinations of two or morethereof. The presently preferred organic acid is an organic acid havingthe formula of HO₂CACO₂H in which A is an alkylene group, an arylenegroup, alkenylene group, or (4) combinations of two or more thereof.Each A has about 2 to about 30, preferably about 3 to about 25, morepreferably about 4 to about 20, and most preferably 4 to 15 carbon atomsper group. Examples of suitable organic acids include, but are notlimited to, terephthalic acid, isophthalic acid, naphthalic acid,succinic acid, adipic acid, phthalic acid, glutaric acid, acrylic acid,oxalic acid, benzoic acid, maleic acid, propenoic acid, and combinationsof two or more thereof. The presently preferred organic diacid isterephthalic acid because the polyesters produced therefrom have a widerange of industrial applications. Examples of suitable esters include,but are not limited to, dimethyl adipate, dimethyl phthalate, dimethylterephthalate, methyl benzoate, dimethyl glutarate, and combinations oftwo or more thereof.

Examples of carboxylic acid metal salts or esters thereof includes a5-sulfo isophthalate metal salt and its ester having the formula of(R²O₂C)₂ArS(O)₂OM in which each R² can be the same or different and ishydrogen or an alkyl group containing 1 to about 6, preferably 2, carbonatoms. Ar is a phenylene group. M can be an alkali metal ion such assodium. An example of the ester is bis-glycolate ester of 5-sulfoisophthalate sodium salt.

Any alcohol that can esterify an acid to produce an ester or polyestercan be used in the present invention. The presently preferred alcoholhas the formula of R(OH)_(n), an alkylene glycol of the formula(HO)_(n)A¹(OH)_(n), or combinations thereof in which R is the same asthat disclosed above; n is a number of 1 to about 10, and preferably 1to 5; and A¹ is an alkylene group having 2 to about 10, preferably 2 to7, and most preferably 2 to 4, carbon atoms. Examples of suitablealcohols include, but are not limited to, ethanol, propanol,isopropanol, butanol, ethylene glycol, propylene glycol, isopropyleneglycol, butylene glycol, 1-methyl propylene glycol, pentylene glycol,diethylene glycol, triethylene glycol, 2-ethyl hexanol, and combinationsof two or more thereof. The presently most preferred alcohol is analkylene glycol such as ethylene glycol for the polyester producedtherefrom has a wide range of industrial applications.

The contacting of an organic acid and alcohol in the presence of thecatalyst can be carried out by any suitable means. For example, theorganic acid and alcohol can be combined before being contacted with thecatalyst. Also for example, the catalyst can be first dissolved in analcohol by any suitable means such as mechanical mixing or stirringfollowed by combining the solution with (1) a carbonyl compound and (2)an alcohol under a condition sufficient to effect the production of anester or polyester. In the preparation of a polyalkylene terephthalate,it is preferred that the aqueous catalyst solution be dissolved in analkylene glycol and then fed to the reaction mixture.

The oligomer of an organic acid and alcohol generally has a total ofabout 1 to about 100, preferably from about 2 to about 10 repeat unitsderived from the carbonyl compound and alcohol.

Any suitable condition to effect the production of an ester or polyestercan include a temperature in the range of from about 150° C. to about500° C., preferably about 200° C. to about 400° C., and most preferably250° C. to 300° C. under a pressure in the range of from about 0.001 toabout 10 atmospheres for a time period of from about 0.2 to about 20,preferably about 0.3 to about 15, and most preferably 0.5 to 10 hours.

The molar ratio of the alcohol to organic acid can be any ratio so longas the ratio can effect the production of an ester or polyester.Generally, the ratio can be in the range of from about 1:1 to about10:1, preferably about 1:1 to about 5:1, and most preferably 1:1 to 4:1.

The catalyst, expressed as Ti, can be present in the range of about0.0001 to about 30,000 parts per million (ppm) by weight of the mediumcomprising the organic acid and alcohol, preferably about 0.001 to about1,000 ppm, and most preferably 0.001 to 100 ppm. Other ingredients alsocan be present to enhance catalyst stability or performance.

The catalyst composition can be used in producing esters or polyestersby using any of the conventional melt or solid state techniques. Thecatalyst compositions are compatible with conventional esterificationand transesterification catalysts (e.g., manganese and/or cobalt salts)and may be introduced to the production process concurrent with, orfollowing, introduction of the esterification catalyst. The catalystcompositions also have been found to be effective in promoting theesterification reaction, and may be used as a substitute for some or allof the esterification catalyst.

The second embodiment of the invention also provides an antimony-freeprocess for the preparation of polyalkylene terephthalates, whichcomprises combining (1) aqueous solution of a titaniumα-hydroxycarboxylic acid or its salt and (2) aqueous solution of a zincsalt with an alcohol, such as alkylene glycol, to produce a glycolsolution and contacting the glycol solution with a mixture ofterephthalic acid or ester and an alkylene glycol monomer under reactionconditions. While the aqueous solution that results from combiningsolutions (1) and (2) can correspond to that described in the firstembodiment, it is not limited to that composition, i.e., it does nothave to be a single, storage-stable solution.

Alternatively, the process for the preparation of polyalkyleneterephthalates can comprise combining (a) aqueous solution of a titaniumα-hydroxycarboxylic acid or its salt in an alcohol and (b) aqueoussolution of a zinc salt in an alcohol, wherein the alcohol used toprepare the titanium or zinc solution is an alkylene glycol, to producea glycol solution and contacting the glycol solutions with a mixturecomprising an organic acid disclosed above such as terephthalic acid orester thereof and a second alkylene glycol under esterification,transesterification, or polycondensation conditions. Furtheralternatively, solutions (a) and (b) can be separately combined with amixture comprising an organic acid or ester and an alkylene glycolmonomer under esterification, transesterification, or polycondensationconditions. The definition of titanium, α-hydroxycarboxylic acid, zincsalt, and alcohol and quantities thereof can be the same as thosedisclosed above. Optionally, various stabilizing agents, color toners,co-catalysts or other ingredients can be included in the process, eitherseparately or as part of the above aqueous solutions.

The invention process can also use a soluble cobalt compound such ascobalt acetate to aid the catalysis and improve the color of the finalpolymer by acting as a toner. The amount used is preferably from zero upto about equal weight of titanium used. It can conveniently be added aspart of the inventive catalyst solution providing the amount added doesnot interfere with solution stability.

The invention process can also use a phosphorus compound to improve thecolor of the final polymer. While any of the many known phosphorus colorinhibitors for preparation of polyalkylene terephthalates can be used,phosphoric acid is preferred for its ready availability. The phosphoricacid can be added separately, or as part of the aqueous solution. Theamount of phosphorus compound added may be up to about 15 weight %phosphorus relative to the solution, providing it does not interferewith solution stability.

Phosphorus acts to reduce catalyst effectiveness. Preferably it is addedafter the esterification or transesterification step is completed. Forexample, when using terephthalic acid and ethylene glycol to makepolyethylene terephthalate by the esterification route, a catalyst istypically only required for the polycondensation step, and thephosphorus compound can be part of the aqueous catalyst solution for thepolycondensation. When using dimethyl terephthalate and ethylene glycolto make polyethylene terephthalate by the transesterification route,manganese compounds are typically the transesterification catalyst ofchoice. The use of manganese may cause formation of some undesirablecolor. The addition of a phosphorus compound can reduce this colorproblem, and can be added as part of the inventive catalyst solution forthe polycondensation step.

Generally, the preferred molar ratio can be 2≦Zn/Ti≦30 and, ifphosphorus and cobalt are used, 1≦(Ti+Zn+Co)/P≦20.

A process of particular commercial importance is the production ofpolyethylene terephthalate. This is typically carried out by one of tworoutes: the transesterification of dimethyl terephthalate (DMT) withethylene glycol followed by polycondensation, and the esterification ofterephthalic acid (TPA) with ethylene glycol followed bypolycondensation.

In DMT-based technology, manganese is preferably used astransesterification catalyst in the amount of about 80 to 160 ppm,preferably about 100 to about 120 ppm based on the total quantity ofterephthalic acid. When transesterification is complete a phosphoruscompound, about 0.1 to about 100 ppm P based on the total quantity ofterephthalic acid can be added to deactivate the manganese. Thenantimony (about 200 ppm based on the total quantity of terephthalicacid) or titanium (about 20 ppm based on the total quantity ofterephthalic acid) can be used for the polycondensation step.

The inventive aqueous catalyst composition can be used in the DMT-basedprocess in several ways. It can be added in the transesterification stepto substitute for all or part of the manganese to obtain a fastertransesterification. Phosphorus can be added to eliminate any manganeseused. The inventive catalyst solution can also be used in thepolycondensation step to eliminate the use of antimony or to reduce theamount of titanium and its related color problems. The use of zincpermits the amount of titanium to be reduced by about 50% to minimizecolor in an ester or polyester associated with higher concentrations oftitanium. If necessary to improve the color, about 0.1 to about 100 ppmof cobalt can be added to act as a color toner.

The inventive catalyst solution can also be used in the TPA-basedprocess. It can be added prior to esterification if there is a need tospeed up this step. Any phosphorus needed can be added afteresterification. Alternatively, the inventive catalyst solution can beadded after esterification to the resulting oligomer. As with theDMT-based process, it can be used in the polycondensation step toeliminate the use of antimony or to reduce the amount of titanium andits related color problems. If necessary to improve the color, about 0.1to about 100 ppm of cobalt can be added as toner.

The following Examples are provided to further illustrate the presentinvention and are not to be construed as to unduly limit the scope ofthe invention. All TYZOR® products noted in the examples were obtainedfrom DuPont, Wilmington, Del., USA.

EXAMPLE 1

This example shows failure to add a carboxylic acid results in anunstable solution.

An aqueous zinc salt solution is prepared by adding 154.6 grams of zincacetate to 340 grams of water and heating to a temperature of about35-40° C. To this solution, 76 grams of an aqueous solution of titaniumbis-sodium lactate containing 7.6% titanium, by weight, is slowly addedover a period of 30 minutes. During the addition, the solution becomescloudy. The cloudy solution is divided.

To one half of the solution is added 6.2 grams of lactic acid. Thissolution becomes clear over a period of 30 minutes.

The untreated solution remains cloudy, indicating the solution isunstable absent the addition of acid.

The process is repeated with addition of an alkanolamine,triethanolamine, and an aminocarboxylic acid, glycine instead of lacticacid. Both solutions remain cloudy after the respective additions of thetriethanolamine and glycine.

EXAMPLE 2

The following solutions were prepared by mixing ingredients shown inTable 1, combining ingredients in any order and mixing by manualstirring at room temperature (about 25° C.), with the weight shown ingrams. The solutions were then stored at 60° C. to provide anaccelerated aging test, and periodically examined for signs ofinstability. Results are shown below. TABLE 1 Composition of TestSolutions A to G Compound A B C D E F G 1) TYZOR ® LA 244 244 244 244244 244 244 2) Zinc acetate 537 537 403 403 268 268 403 3) Water 12001200 800 800 538 538 800 4) Lactic Acid 0 43 0 33 0 22 0 5) Acetic Acid0 0 0 0 0 0 25

The storage stability tests (by visual observation) showed that SolutionA gelled overnight at 60° C., while Solution B containing lactic acidwas storage stable at 60° C. for 4 weeks. Similarly Solution C gelled in3 days at 60° C., while Solution D containing lactic acid wasstorage-stable at 60° C. for 4 weeks. Solution E became cloudy after 21days at 60° C., while Solution F containing lactic acid wasstorage-stable at 60° C. for 4 weeks. Solution G was also storage-stableat 60° C. for 4 weeks.

The above tests show that a stable aqueous solution can be prepared bymixing a titanium bis-ammonium lactate complex with lactic acid oracetic acid, zinc acetate and water. If the lactic acid or acetic acidis left out, the mixture will gel or cloud up under accelerated storageconditions (60° C.).

EXAMPLE 3

This example shows runs using the inventive catalyst and process.

The process for producing terephthalic acid-based polymer is illustratedas follows. A 1-liter resin kettle was provided with a Jiffy Mixeragitator rotating at 40 rpm, a thermocouple, condenser and nitrogensweep. To this kettle was added the catalyst to be tested, 115 ml ofethylene glycol, and 400 g of terephthalic acid oligomer prepared above.The agitator was turned on and the temperature was increased to 275° C.over a period of about 2.5 hours. The contents were polymerized byholding under agitation at 275° C. and a pressure of 120 mm Hg for 20minutes, and at 280° C. and a pressure of 30 mm Hg for an additional 20minutes. The contents were then held under agitation at 285° C. at 1 to2 mm Hg pressure for a time sufficient to reach 15 ounce-inch (0.106Newton-meter) torque as measured by an Electro-Craft Motomatic torquecontroller. The time for this step was recorded as the Finish Time, andvaried with the catalyst used. The polymer melt was then poured into awater bath to solidify the melt, and the resultant solid annealed at150° C. for 12 hours and ground to pass through a 2 mm filter for colormeasurements using the previously described spectrophotometer. Resultscomparing the color as measured spectrophotometrically are given inTable 2 below.

Color of the resulting polymer was measured in terms of the L-value andb-value, using an instrument such as the SP-78 Spectrophotometer. TheL-value shows brightness, with the greater the numerical value showinghigher (desirable) brightness. A value of 78 or more would be consideredgood. It will vary with additives such as cobalt.

The b-value shows the degree of yellowness, with a higher numericalvalue showing a higher (undesirable) degree of yellowness. For thelaboratory trials, b colors below 7 would be considered a success. Plantvalues are different because of differences in methods of processcontrol, additives, etc. For plant trials, results within 2 b units ofan antimony standard would be considered a success. Prior art may showdifferent L and b values depending on scale of operation, quality ofoligomer, quality of recycled glycol, additives, air leakage in system,control of process, and other factors. The only consistent way tomeasure results is by direct comparison with an antimony standard or aprior art catalyst under comparable conditions.

The following solutions were used as catalysts or additives to theprocess.

Catalyst solution A was made by dissolving 224 g titanium bis-ammoniumlactate solution, 22 g lactic acid, and 123 g of zinc acetate in 270 gmof water, followed by agitation to dissolve the zinc acetate.

Catalyst solution B was made by dissolving 224 g titanium bis ammoniumlactate solution, 43 g lactic acid, and 432 g zinc acetate in 1035 g ofwater, followed by agitation to dissolve the zinc acetate.

Catalyst solution C was made-by dissolving 432 g zinc acetate in 1035 gof water, followed by agitation to dissolve the zinc acetate.

Table 2 shows that the use of mixtures of aqueous solutions of organiccomplexes of titanium and zinc had high catalytic activity and producedesters and polyesters with excellent color value compared to use of zincor titanium separately. TABLE 2 Performance of Catalyst Compositions RunTi(ppm) Zn(ppm) Co(ppm) P(ppm) Time(min) L color b color Footnote 1C 1020 10 65 79.39 8.02 2 2E 10 20 10 35 80.85 6.14 3 3C 10 20 5 80 77.507.16 2 4E 10 20 5 70 79.05 6.30 3 5C 70 105 83.07 4.84 6 6C 25 65 77.309.12 7 7E 10 70 50 78.89 6.43 4 8C 10 70 50 65 78.53 8.97 4 and 5 9E 1070 10 55 82.46 5.79 41 E indicates an invention example and C indicates a comparativeexample.2 Runs 1 and 3 were run with ethylene glycol solution of the individualcomponents; the remaining examples were run with aqueous solutions ofthe mixed components following the inventive process.3 Runs 2 and 4 were run with catalyst solution A.4 Runs 7 and 9 were run with catalyst solution B.5 Run 8 was run using 110 ppm Mn and catalyst solution B.6 Run 5 was run using catalyst solution C.7 Run 6 was run using an aqueous solution of titanium bis-ammoniumlactate.

Table 2 shows that using mixtures of aqueous solutions of organiccomplexes of titanium and zinc had high catalytic activity (shorterreaction time for Runs 2 and 4 vs. 1 and 3) and produced products withlow b color value.

Runs 7 and 9 show the synergism of using Ti in combination with zinccompared to Ti (Run 6) or zinc (Run 5) separately. Zinc by itself (Run5) was too slow. Using Ti only (Run 6) required a higher Ticoncentration (25 ppm vs 10 ppm) to get similar activity to Run 7 andproduced a product that had a higher b value (9.12 vs. 6.43). Runs 7 and9 show that by combining low levels of Ti with zinc, good catalyticactivity and product color were obtained.

Run 9 differed from Run 7 in that 58 g of phosphoric acid was tocatalyst solution B. The addition of 10 ppm P to the mixture of 10 ppmTi and 70 ppm Zn decreased reaction rate slightly, but improved b.

Run 8 shows the effect of adding a mixture of Ti and zinc (catalyst B)to an oligomer made using 120 ppm manganese and 50 ppm P. The use ofmanganese in combination with catalyst B gave (resulted in) a producthaving (a) much higher b color (8.97 vs.6.43).

1. A solution composition comprising (a) titanium in the form of atitanium α-hydroxycarboxylic acid or its salt, (b) a C₁-C₆ aliphaticcarboxylic acid, (c) zinc in the form of a water-soluble zinc salt, and(d) water; and wherein the solution is substantially free of analkanolamine, an aminocarboxylic acid, or combinations two or morethereof and stable for at least 2 weeks under accelerated agingconditions.
 2. A composition according to claim 1 further comprisingphosphorus in the form of a water-soluble phosphorus compound.
 3. Acomposition according to claim 2 wherein the molar ratio of (titaniumplus zinc) to phosphorus is greater than about 1.5.
 4. A compositionaccording to claim 1 further comprising a water-soluble cobalt compound.5. A composition according to claim 3 further comprising a water-solublecobalt compound.
 6. A composition according to claim 1 wherein saidα-hydroxycarboxylic acid is citric acid, lactic acid, malic acid,tartaric acid, glycolic acid, glyceric acid, α-hydroxybutyric acid,α-hydroxypropionic acid, or combinations of two or more thereof.
 7. Acomposition according to claim 6 wherein said C₁-C₆ aliphatic carboxylicacid is formic acid, acetic acid, propionic acid, butyric acid,pentanoic acid, hexanoic acid, citric acid, lactic acid, malic acid,tartaric acid, glycolic acid, glyceric acid, α-hydroxybutyric acid,α-hydroxypropionic acid, or combinations of two or more thereof.
 8. Acomposition according to claim 7 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.9. A composition according to claim 3 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.10. A composition according to claim 5 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.11. A composition according to claim 7 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-sodium lactate. 12.A composition according to claim 3 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-sodium lactate. 13.A composition according to claim 5 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-sodium lactate. 14.A composition according to claim 1 wherein said C₁-C₆ aliphaticcarboxylic acid is lactic acid.
 15. A composition according to claim 3wherein said C₁-C₆ aliphatic carboxylic acid is lactic acid.
 16. Acomposition according to claim 9 wherein said C₁-C₆ aliphatic carboxylicacid is lactic acid.
 17. A composition according to claim 10 whereinsaid C₁-C₆ aliphatic carboxylic acid is lactic acid.
 18. A compositionaccording to claim 1 wherein said water-soluble zinc salt is zincacetate.
 19. A composition according to claim 11 wherein saidwater-soluble zinc salt is zinc acetate.
 20. A composition according toclaim 12 wherein said water-soluble zinc salt is zinc acetate.
 21. Acomposition according to claim 14 wherein said water-soluble zinc saltis zinc acetate.
 22. A composition according to claim 1 wherein thesolution contains about 5 to about 30 weight % titanium bis-ammoniumlactate, about 1 to about 5 weight % lactic acid, and about 20 to about30 weight % zinc acetate.
 23. A process comprising contacting, in thepresence of a catalyst, (1) an organic acid or its salt or its esterwith (2) an alcohol wherein said catalyst comprises (a) titanium in theform of a titanium α-hydroxycarboxylic acid or its salt, (b) a C₁-C₆aliphatic carboxylic acid, (c) zinc in the form of a water-soluble zincsalt, and (d) water; and wherein the solution is substantially free ofan alkanolamine, an aminocarboxylic acid, or combinations two or morethereof and stable for at least 2 weeks under accelerated agingconditions.
 24. A process according to claim 20 wherein saidα-hydroxycarboxylic acid is citric acid, lactic acid, malic acid,tartaric acid, glycolic acid, glyceric acid, α-hydroxybutyric acid,α-hydroxypropionic acid, or combinations of two or more thereof.
 25. Aprocess according to claim 21 wherein said C₁-C₆ aliphatic carboxylicacid is formic acid, acetic acid, propionic acid, butyric acid,pentanoic acid, hexanoic acid, citric acid, lactic acid, malic acid,tartaric acid, glycolic acid, glyceric acid, α-hydroxybutyric acid,α-hydroxypropionic acid, or combinations of two or more thereof.
 26. Aprocess according to claim 22 wherein said catalyst further comprisesphosphorus in the form of a water-soluble phosphorus compound.
 27. Aprocess according to claim 23 wherein the molar ratio of (titanium pluszinc) to phosphorus is greater than about 1.5.
 28. A process accordingto claim 22 further comprising a water-soluble cobalt compound.
 29. Aprocess according to claim 24 further comprising a water-soluble cobaltcompound.
 30. A process according to claim 22 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.31. A process according to claim 24 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.32. A process according to claim 26 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-ammonium lactate.33. A process according to claim 22 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-sodium lactate. 34.A process according to claim 24 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-sodium lactate. 35.A process according to claim 26 wherein said titaniumα-hydroxycarboxylic acid or its salt is titanium bis-sodium lactate. 36.A process according to claim 22 wherein said C₁-C₆ aliphatic carboxylicacid is lactic acid.
 37. A process according to claim 23 wherein saidC₁-C₆ aliphatic carboxylic acid is lactic acid.
 38. A process accordingto claim 27 wherein said C₁-C₆ aliphatic carboxylic acid is lactic acid.39. A process according to claim 28 wherein said C₁-C₆ aliphaticcarboxylic acid is lactic acid.
 40. A process according to claim 22wherein said water-soluble zinc salt is zinc acetate.
 41. A processaccording to claim 30 wherein said water-soluble zinc salt is zincacetate.
 42. A process according to claim 31 wherein said water-solublezinc salt is zinc acetate.
 43. A process according to claim 33 whereinsaid water-soluble zinc salt is zinc acetate.
 44. A process according toclaim 22 wherein said solution comprises or is produced by combiningabout 5 to about 30 weight % titanium bis-ammonium lactate, about 1 toabout 5 weight % lactic acid, and about 20 to about 30 weight % zincacetate.
 45. A process according to claim 38 wherein said organic acidis terephthalic acid, said ester is dimethyl terephthalate, and saidalcohol is ethylene glycol.
 46. A process comprising contacting, in thepresence of a stable solution, an organic acid or its salt or its esterwith an alcohol wherein said stable solution comprises or is produced bycombining about 5 to about 30 weight % titanium bis-ammonium lactate,about 1 to about 5 weight % lactic acid, and about 20 to about 30 weight% zinc acetate, based on the total weight of said organic acid; saidorganic acid or its salt or its ester is terephthalic acid or dimethylterephthalate; and said alcohol is ethylene glycol.
 47. A processaccording to claim 40 wherein the molar ratio of Zn to Ti is in therange of from 2 to
 30. 48. A process according to claim 41 wherein saidprocess is carried out in the presence of a phosphorus compound.
 49. Aprocess according to claim 42 wherein said process is carried out in thepresence of a cobalt compound and the molar ratio of (Ti+Zn+Co)/P isfrom 1 to 20.